After failing to persuade a magistrates and the court of appeal that the cross border warrant issued for his arrest was invalid, the Australian's legal team will appeal to the supreme court in London to prevent his deportation.

Assange is wanted for questioning in Sweden over claims of rape, sexual molestation and unlawful coercion made by two women he met on a visit to Stockholm in August 2010. He denies the claims.

The supreme court's two-day hearing is unlikely to focus on the detail of the allegations against him, but the legal issue of whether the Swedish prosecutor who issued the European arrest warrant in December 2010 can be considered a valid judicial authority. Assange's legal team, which will include Dinah Rose QC, an expert in civil liberties and European Union law, argues that it isn't.

In Britain, as in the United States, only judges can normally approve arrest warrants. In Assange's case, the warrant was issued by Sweden's public prosecutor. Assange's lawyers argue that the Swedish system is unfair because it puts the power to issue arrest warrants in the hands of the same people who are prosecuting him.

Seven judges rather than the usual five will hear the case "given the great public importance of the issues raised", the court said. Their decision is not expected for several weeks.

Legal observers have suggested Assange faces an uphill struggle. Karen Todner, an extradition specialist at Kaim Todner Solicitors, said Assange's lawyers were unlikely to overcome the benefit of the doubt usually afforded to other European countries' judicial systems.

British judges "absolutely defer" to their European counterparts' justice systems, she said, adding that she would be "very surprised" if Assange's team won the day.

European arrest warrants are difficult to beat, and Caldwell argued that while Assange's case was "well-argued ... it doesn't get beyond the obligation of the UK to give effect to European law."

Julian Knowles QC, a specialist extradition barrister based at Matrix Chambers, has said an Assange win would mean that until the law was rewritten, extradition to Europe would become very difficult if not impossible.

In the background is the US investigation into WikiLeaks, which could potentially see Assange charged with espionage or other offences. His supporters fear that extradition to Sweden could be a prelude to an extradition to the US.